The present invention relates to a method for producing a Fe-based amorphous alloy ribbon, and to a method for producing a nanocrystalline material from the Fe-based amorphous alloy ribbon.
As a method for producing an amorphous alloy ribbon, molten alloy-quenching methods such as a single roll method, a twin roll method, a centrifugal quenching method, etc. have been widely known. Among the methods, preferred from the viewpoints of productivity and easy maintenance is the single roll method, wherein the amorphous alloy ribbon is obtained by ejecting a molten alloy onto a cooling roll rotating at a high speed to rapidly solidify the molten alloy.
A nanocrystalline material can be produced by subjecting the amorphous alloy ribbon obtained by such a method to a heat treatment. Typical Fe-based nanocrystalline materials have a composition such as Fexe2x80x94Sixe2x80x94Bxe2x80x94(Nb, Ti, Hf, Mo, W, Ta)xe2x80x94Cu, Fexe2x80x94(Co, Ni)xe2x80x94Cuxe2x80x94Sixe2x80x94Bxe2x80x94(Nb, W, Ta, Zr, Hf, Ti, Mo), Fexe2x80x94(Hf, Nb, Zr)xe2x80x94B, Fexe2x80x94Cuxe2x80x94(Hf, Nb, Zr)xe2x80x94B, etc. described in Japanese Patent Publication No. 4-4393, Japanese Patent Publication No. 7-74419, Japanese Patent No. 2812574, etc.
The nanocrystalline material has an excellent heat stability compared with the amorphous alloy, and exhibits a little change with time in properties thereof, a low magnetostriction and a high permeability, thereby being used for a common-mode choke coil, a pulse transformer, an circuit breaker, etc.
It is important for the amorphous alloy ribbons used as a precursor for the nanocrystalline materials to have no crystalline phase before the heat treatment. A crystalline phase formed in the amorphous alloy ribbon before the heat treatment, for example while casting, comprises crystal grains extremely larger than those formed in a homogeneous amorphous phase by the heat treatment. In the case where the amorphous alloyxe2x80x94ribbon partially comprising the extremely larger crystal grains is heat-treated to produce the nanocrystalline material, the resultant nanocrystalline material fails to have a uniform structure to show increased crystalline magnetic anisotropy, thereby being poor in soft magnetic properties. Thus, it is desirable that the molten alloy is quenched as rapidly as possible to prevent the amorphous alloy from crystallization.
However, in the case where the molten alloy is quenched too rapidly, the amorphous alloy tends to be broken in the course of producing the amorphous alloy ribbon, so that the ribbon cannot be continuously obtained. Further, although the amorphous alloy ribbon is generally wound in a toroidal core shape to use, the breakage of the alloy makes it difficult to produce the core continuously.
An object of the present invention is to provide a method for stably producing a Fe-based amorphous alloy ribbon having no crystalline phase without breakage continuously, and a method for producing a nanocrystalline material excellent in soft magnetic properties from the Fe-based amorphous alloy ribbon.
As a result of intense research in view of the above object, the inventors have found that a solidified Fe-based alloy containing 10 atomic % or less of B is peeled from a cooling roll at a controlled temperature, to stably, continuously obtain a Fe-based amorphous alloy ribbon without breakage. The present invention has been accomplished by the finding.
Thus, a method for producing a Fe-based amorphous alloy ribbon according to the present invention comprises the steps of: ejecting a molten Fe-based alloy containing 10 atomic % or less of B onto a cooling roll to solidity the molten Fe-based alloy; and peeling the solidified Fe-based alloy from the cooling roll when the solidified Fe-based alloy has a temperature of 100 to 300xc2x0 C. Incidentally, the term xe2x80x9cnanocrystalline materialxe2x80x9d as used in the present invention means a material comprising crystal grains having an average grain diameter of 300 nm or less, preferably 100 nm or less.
In a method for producing a nanocrystalline material according to the present invention, the Fe-based amorphous alloy ribbon obtained by the above method is subjected to a heat treatment at a temperature equal to or more than a crystallization temperature of the Fe-based amorphous alloy ribbon, to produce the nanocrystalline material.
To make crystal grains in the nanocrystalline material fine, the molten Fe-based alloy preferably contains 15 atomic % or less of group 4A, 5A and/or 6A element. Further, the molten Fe-based alloy may contain preferably 0.5 to 15 atomic %, more preferably 1 to 10 atomic % of Nb. Furthermore, the molten Fe-based alloy preferably contains 0.1 to less than 4 atomic % of Cu, and/or 5 to 25 atomic % of Si.
It is particularly preferable that the molten Fe-based alloy has a composition comprising 2 to 10 atomic % of B, 1 to 5 atomic % of Nb, 0.1 to 3 atomic % of Cu, 10 to 20 atomic % of Si and the balance being substantially Fe. The Fe-based amorphous alloy ribbon preferably has a thickness of 8 to 25 xcexcm.
The solidified Fe-based alloy is peeled from the cooling roll when the solidified Fe-based alloy has a temperature of preferably 100 to 250xc2x0 C., more preferably 150 to 250xc2x0 C.